Given that deep base vibrations are generally found to be sympathetic to the listener, in order to enhance the audio component of an entertainment system a number of systems have been proposed which convert the bass audio signal to a vibration. These systems typically include a transducer, motor or other mechanical device which is capable of converting the audio input signal into a vibration. As a result, instead of or in addition to being heard, the bass signal is perceived through tactile senses.
Additionally, imparting a vibration to the viewer of a moving image which is synchronized with the moving image provides an additional dimension which can be exploited in order to enhance the viewing experience. Therefore, a variety of entertainment and simulation systems have been proposed which combine projected images with synchronised movement and vibrations. The prior art reveals systems which use high intensity, low frequency noise synchronized to a projected moving picture film or video to produce physiological sensations, for example a shaking sensation to simulate the effect of an earthquake, in the audience. Earlier prior art systems conduct movement or vibrations to a seated, or in some cases standing, viewer or viewers by a variety of mechanical means, including those based on the control of compressed air or hydraulics.
The introduction of multi-track digital audio combined with moving picture film or high resolution video projectors has lead to an increase in the common place combination of moving projected images with complex and high quality directional hi-fidelity audio sound tracks. In a home entertainment system, for example, typically five (5) audio channels are used to supply input to four (4) satellite speakers positioned around the viewer and a single front speaker while a sixth audio channel is used to supply a lower frequency subwoofer bass speaker. In some cases a high intensity, low frequency sound supplied to the bass speaker provides the viewer with the sensation of vibrations. In order to further amplify the vibrations a variety of acoustic transducers have been proposed which, when supplied with an appropriate low frequency audio signal, generate high intensity vibrations which can be perceived through tactile senses but not heard.
Known in the art are acoustic transducers where the moving element is deflected in a direction generally perpendicular to a rigid surface to which the transducer is attached. The prior art also discloses acoustic transducers which are securely mounted to a hard relatively flat surface, for example a floor, a chair back or underneath the base of a chair. The transducers use the surface to which they are mounted as a means for transmitting vibrations to a person or persons in contact with the surface. These prior art acoustic transducers generate vibrations either percussively, for example by repeatedly rapping the cam of a solenoid against the hard flat surface, or by accelerating a relatively large mass back and forth relative to the surface. In both these prior art assemblies the movement of the cam or the mass is perpendicular to the surface to which the acoustic transducer is attached.
One drawback of the above prior art acoustic transducers is that the transducer has a characteristically uneven frequency response with a dominant resonant frequency being generally excited when the surface is struck. This frequency is independent of the frequency or force with which the surface is hit. Still another drawback is that the vibrations propagate in only a limited manner and therefore in large installations such as cinemas a large number of transducers are needed in order to convey the vibrations to the entire audience. An additional drawback is that in all installations in order to successfully induce vibrations the acoustic transducer(s) must be securely mounted to a rigid surface which leads to difficulties in installation and removal, especially for home applications.